Conversion of hydrocarbons



PERCENT OF PRODUC T March'zo, 1945. R. F; RUTHRUFF 2,372,018

CONVERS ION OF HYDROCARBONS Filed June 7, 1939 4 Sheets-Sheet 1 0 l I ll l 1 Z 4 6 8 I0 l2 l4 l6 I8 20 TIME MINUTES w F/GU/FE B ,5 50- k K 40-F2 R30- #1 a? Lu 20 0 I l I I l l TIME MINUTES ROBE/FT F HUT/{RUFF ill;INVENTOR @WW ATTORN EY March 20, 1945. RUTHRUFF 2,372,018

CONVERSION OF HYDROCARBONS Filed June 7, 1939 '4 Sheets-Sheet 2 F/G. LU

INVENTOR ROBERT F. RU-THRUFF Mun-.4,

ATTORNEY 4 Sheets-Sheet 4 Filed June 7, 1939 R Q Q INVENTOR RObERT F.RUTHRUFF BY uMB hlh? ATTORNEY Patented Mar. 20, 1945 uN TEo STATESPATENT OFFICE" CONVERSION OF HYDROCA RBONS Robert F. Rnthruil', Nutley,N. .L, assignor to The M. W. Kellogg Company, New York, N. Y., a'corporation of Delaware Application June 7, 1939, Serial No. 277,885

Claims.

perature, decomposition or cracking sets in with the production ofvarious conversion products.

When, for example, a mixture of liquid hydrocarbons boiling in thetemperature range 400-750 F., is thermally cracked or decomposed, thefollowing conversion products are obtained; gas, gasoline, cycle stockhaving approximately the same boiling range as the hydrocarbon charge,

tar and coke. By returning the cycle stock to the conversion zone, gas,gasoline, tar and coke are obtained as ultimate conversion products.Usually, gasoline is the desired decomposition product while gas, tarand coke are, under most circumstances, undesirable.

Many advantages follow the use of contact materials or catalysts inthedecomposition or cracking of hydrocarbons. For example, the operatingtemperature required for a given amount of conversion may beconsiderably lowered in comparison with the temperatures required inoperations conducted in the absence of catalysts. Additionally, thequality of the gasoline produced in the presence of catalysts is higherthan that of thermally cracked gasoline and also the yield of thissuperior product is'enhanced. In catalytic cracking, gas, gasoline,cycle stock and coke are produced, so the ultimate products are gas,gasoline and coke. It will be observed that in catalytic cracking, notar is usually produced although it is The coke produced duringcatalytic conversion "progressively increases throughout the conversion,and-finally reaches a stage at which it deactivates the catalyst to anextent necessitating its regeneration; Regeneration is usually efiectedby passing air over the spent catalyst and burning oil the depositedcoke at a suitable temperature. A great variety of catalytic materials,differing widely in physical structure and chemical composition havebeen suggested for use as cracking catalysts, and in each instance,these materials have been recognized as requiring periodic regenerationtreatments for removal of deposited to be noted that generally the cokeproduction in catalytic cracking is appreciably greater than in thermalcracking and this enhanced coke production may be considered equivalentto part of the tar produced in thermal cracking.

While the catalytic conversion of hydrocarbons is superior to thermalprocesses, the former operatibn is not perfect for here too, undesirableproducts (gas and coke) are formed. By the practice of this inventionthe production of these undeslrable products is decreased, while theproduction of gasoline is increased.

carbonaceous material in order to enable them to be employed forrepeated conversion treatments.

The basis of this invention resides in the observation and discoverythat, the alumina-silica type of cracking catalyst exhibits certaindistinctive phenomena during the initial portion of the conversion cyclewith respect to the products produced, and in the provision of a processarising from this observation whereby a more favorabledistribution andenhanced yield of the desired conversion products is obtained.

The catalytic material contemplated for use in the practice oi. theinvention comprises. either. naturally occurring or syntheticallyprepared mixtures or compounds of silica and alumina,

suitably prepared so as to exhibit a high degree of catalytic crackingactivity. A variety of difierent methods for the preparation ofcatalysts of this type have been described heretofore in the art. Forexample, a suitable type of aluminasilica cracking catalyst for use inaccordance with my invention may be artificially prepared by im-'pregnating a hydrogel of silica with a heat-decomposable salt of aluminasuch aluminum nitrate, and then'heating the impregnated hydrogel todecompose the nitrate, thereby producing a suitable cracking catalystconsisting of a hard porous silica gel impregnated with alumina, thismethod of preparation being that described in U. S. Patent 1,782,857.Other materials containing alumina and silica such as naturallyoccurring, or activatedadsorbent clay materials such as for examplei'ullers earth and bentonite, having the eflfect of catalyticallyconverting the higher-boiling hydrocarbons into lower one, may

be employed. An activated bleaching clay sold under suitable conditionsand thereafter removing the products or reaction by successive washingswith large volumes of hot water. After dewatering, the pulp is driedunder carefully controlled conditions followed by final grinding todesired mesh specification.

The term alumina-silica cracking catalyst as employed herein and in theappended claims, designates and is limited to a well recognized class ofmaterials known for their capability of catalyzing the conversion ofhigh boiling hydrocarbons to lower boiling hydrocarbons within thegasoline boiling range characterized by both high yield and quality ofthe gasoline product. This catalytic conversion is further characterizedby the continuous conversion during the catalytic contact of a portionof the charge to produce a carbonaceous deposit on the catalyst.Activated clays such as Super-Filtrol and synthetic composites includingsilica-gel and alumina are well known examples of this class of catalystmaterial.

Other materials such as pumice, although including alumina. and silicain some form, are known to lack catalytic activity of the characterreferred to and are, therefore, expressly excluded from the termalumina-silica cracking catalyst.

The procedure employed in the practice of my invention, and its variousfeatures and advantages will be apparent from the following detaileddescription thereof, given in connection with the appended drawings,wherein:

Figures 1 and 2 are graphical representations of the per centproduction, based on the hydrocarbon charged, of the various products ofoncethrough catalytic cracking over alumina-silica type of crackingcatalysts, asa function of the catalystexposure time; and

Figures 3, 4, and 5, each illustrates diagrammatically a suitable typeof apparatus for the practice of specific embodiments'of the invention.Referring to Figures 1 and 2', the curves shown are graphicalrepresentations of the instantaneous yields of the per cent production,relative to feed stock, of the conversion products produced by passageof the feed in a once-through operation over alumina-silica type ofcracking catalysts as a function of the catalyst exposure or contacttime. Referring to the individual curves, curve A, represents cokeyield; B, yield of gaseous material; C, yield of cycle stock; and D,yield of gaso-; line. It is to be noted that the yields shown are notcumulative, but rather represent the instantaneous yields obtainedduring any given period of catalyst life, For example, the yield datashown at ten minutes represent the production of conversion productsobtaining at the instant when of itself the true cracking catalyst butthat it is a, material capable of producing carbon or car-- the reactorcontaining the catalyst has been onstream ten minutes, and not thecumulative yield over the first ten minutes of the conversion cycle. Thespecific data shown in Figure 1 were obtained when passing West Texasgas oil over a catalyst consisting of an acid treated clay of the"Super-Filtrol type. A temperature of 850? F. was employed and thechargejwas passed at a rate of 0.3 liquid volume per volume of catalystper hour.

The results in Figure 1 show that when using this catalyst, initially nogasoline or cycle stock is formed, only large amounts of coke and gas.

As time on-stream increases, the yields of gas and coke both decreaserapidly, the yield of cycle stock increases slowly while gasolineproduction rapidly increases to an optimum and then more slowlydeclines.

bonaceous residues of peculiar orientation and properties and that it isthis carbon or these residues that form the true cracking catalyst.During the first few minutes on-stream the major product formed is thisoriented carbon which is of course deposited on thecatalyst. As timegoes on, production of gasoline increases rapidly, reaching a maximum inthe present instance at an on-stream period of approximately tenminutes. At this time, coke production i practically nil while gasproduction is very low. When the on-stream period is increased beyondten minutes, the proportion of gasoline in the reaction productdecreases with increasing rapidity. It is believed that initially thecontact material has little or no ability to make gasoline. As carbon isdeposited on the surfaces of this contact material, this carbon, due toits peculiar orientation and properties which are due t the nature oithe surface of the contact material upon which it is deposited, has theability to convert the charge to gasoline. Conversion to gasolineincreases rapidly as the contact material becomes covered with carbon;likewise as the contact material becomes covered with carbon, lesscharge becomes converted to carbon. However, as cracking progresses, itis believed that tar or pitch forms as a byproduct and this materialalso is deposited on the contact agent, covering the active carbonalready thereon. The tar or pitch or carbonaceous material derivedtherefrom does not, it is believed, possess the required orientationnecessary for converting gas oil to gasoline and accordingly gasolineproduction decreases. As this occurs. the yield of cycle stock increasessimultaneously since there is no fresh surface of contact material toconvert it to coke and no orientated carbonaceous material to convert itto gasoline. Apparently the contact material during any one cycleacquires a double layer. When fresh, the contact material gives largelycoke and gas; when covered with-oriented carbon it produces gasoline;and when the carbon is covered with tar or decomposition productsthereof, the whole is inactive both as a carbon producer and as agasoline producer.

Figure 2 is similar to Figure 1 except that Figure 2 representsconditions'wherein the gas oil charge was passed over the alumina-silicacatalyst at a rate of 1.0 liquid volume-per volume of catalyst per hour.The time on-stream yield relationships in the two figures are quitesimilar, any differences being explainable on the basis of the difierentcharging rates.- In Figure 1, maximum gasoline yield was 73%, attainedwhen the catalyst was on-stream 10.5 minutes. In Figure 2, gasolineyield was maximum at 52.5% when the on-stream period was 2.7 minutes,approximately. The lower gasoline yield in this case refleets theshorter contact time. It will be noted that the increase in gasolineyield to the maximum is faster in Figure 2 than in Figure 1, while thedecline from the maximum is slower. This last is due to the slower rateat which the oriented carbon surface is blanketed with tar or pitch andreflects in turn the lower extent of cracking at the higher charge rate.It appears, however, that the rate of depositing active, oriented carbonon the contact material is not so much a function of contact time. as itis of the total amount of charge passed. For example, in Figure 2,maximum activity was reached in 2.7 minutes. This multiplied by thecharge rate, gives 2.7 volumes of charge passed to reach maximumactivity. In Figure 1, maximum activity was reached in 10.5 minutes andthis multiplied by the charge rate 0.3, gives 3.15 volumes of chargepassed to reach maximum activity. Within the limit of experimentalaccuracy, these two values are substantially identical. I

It may be observed from Figures 1 and 2 that for any length of cycle X,the gasoline yield could be increased if the initial period could be, ineffect, eliminated. In addition, not only is the gasoline yieldincreased but also thegasoilne to gas pluscoke ratio is verysubstantially increased. More specifically, in Figure 1, if the reactionis conducted over the period 6 to minutes shown, the gasoline'yield ishigher than over the period, 0 to 9 minutes, and the gasoline to gasplus coke ratio is much higher. Likewise, in Figure 2, the yield ofgasoline and the product distribution is much more favorable over theperiod, 2 to 6 minutes than the period, 0 to 4 minutes.

It may be further observed that when conducting a catalytic conversionoperation in accordance with the operating conditions obtaining'iorFigure 1, if the products are sent to waste during the initial period,for example, the first five minutes of the reaction cycle after whichthe conversion products are collected for use in the production ofdistillate boiling within the usual gasoline boiling range, the productdistribution in the finally collected products is much improved.However, under such conditions no useful result has been attained sincethe initial product showing poor distribution was sent to waste.

In accordance with my invention the initial period of the cyclecharacterized by undesirable product distribution and yield is, ineifect, eliminated by subjecting the catalyst to a preconditioningtreatmentprior to the conversion reaction. In accordance with thistreatment, a quantity of carbonaceous material is formed or deposited onthe particular type of alumina-silica cracking catalyst employedapproximating the quantity normally deposited during said initial periodabove described. The: quantity of carbon to be thus formed will, ingeneral, range in quantity from about 0.5% to 2.0%, by weight, of thecatalyst, and preferably resides in the somewhat narrower range of about0.8% to 1.5%. Preconditioning of the catalyst, in accordance with myinvention, may be effected by the decomposition of a hydrocarbon mixturewhich is readily broken down or decomposed to produce a mixture ofcarbon and other hydrocarbons by a suitable decomposition treatment, andcontacting the decomposition products with the fresh or regeneratedalumina-silica catalyst in such manner that carbon is deposited thereonto the required extent. Preferably, the conditioning treatment iseffected by passing the hydrocarbons selected for the treatment, incontact with the fresh or regenerated catalyst under reacting conditionsadapted deposit normally deposited during said initial period previouslydescribed, which is characterized by agradually increasing yield oigasoline per unit of time up to an optimum value.

The invention may be practiced with a wide variety of types of catalyticreactors and regeneration equipment. One type involves the socalled"static bed type of operation wherein the catalyst is disposed in thereactorin the form of a stationary or static bed through which the hydrocarbons undergoing treatment are passed. Upon substantialdeactivation of the catalyst, the flow of hydrocarbons thereover isdiscontinued, and ,a regenerating gas such as air is passed over thespent catalyst to burn ofl deposited carbon, Usually a plurality of suchcatalyst reactor chambers are arranged in parallel and suitablymanifolded with respect to the incoming stream of treated hydrocarbonsand regenerating gas, so that the operation is substantially continuous.

. one reactor being on-stream while another is being regenerated.Accordingly, a complete cycle in a given reactor involves both aconversion period and a regeneration period. In accordance with myinventiori the complete cycle includes an additional conditioningperiod. A suitable apparatus for the practice of this embodiment of theinvention is shown in Fgure 3.

Referring to Figure 3, a single reactor I1 is shown, partly in elevationand partly in section. Charging stock, which may consist of reduced"crude or heavy gas oil is passed by line I and pump 2 to furnace 3. Thepreheatedcharge enters separator 4, through line 5, overhead prod uctspassing through line 6 and through opened valve 28 to a reactor orreactors (similar to II, hence not shown) which are exercising thecracking function, valve 1 in line 8 being closed. Heavy products in thepreheated charge accumulate in the bottom of separator 4 from whencethey may be eliminated from the system if desired through valve 3 inline l0.- Alternatively, these heavy products may be passed-throughvalve H in line 12, pump l3 and valve 21 to manifold l4, valve I5 inline l6 being closed. Line 16 leads to manifolds similar to It (notshown) serving to decompose it to a mixture of hydrocarbons the otherreactor or reactors (not shown) exercising, at this stage, the crackingand/or regeneration operations.

Reactor l'l contains a suitable catalyst l8 disposed on a plurality ofperforated trays l9. Manifold M is provided with a plurality of branchedpipes 20, one or more for each tray. If desired, an atomizing fluid,suitably preheated, such as steam, gas made in the process or fromanother source, flue gas made in the regeneration process or from anoutside source, may be passed through line 2! to manifold 22, saidmanifold having a plurality of branched pipes 23, each side pipecorresponding to a side pipe 20 from manifold M.

The heavy charge is distributed to a series oi atomizers or sprays 2t bymeans of the plurality of side pipes 20. Preferablythe atomizers orsprays 24 are disposed inthe layers of catalyst l8 on the perforatedtrays l9 although-they may also be disposed above the catalyst.- Also,itis not necessary to have atomizers or sprays .24 in or near each trayof catalyst. While this arrangement is preferable, satisfactory resultscan be obtained by atomizing, vaporizing or spraying all of the heavycharge in the bottom of reactor -reactor (not shown) which is on thecracking cycle. Passage of the heavy portion of the charge through lineH and decomposition thereof is continued until the desired amount ofcarbon is deposited on the catalyst.

Vaporizable products derived by the decomposition of the heavy portionof the charge leave reactor I! through opened valve 25 in line 26, andmay be disposed of as desired. After a short preconditioning treatment,valve 21 in manifold M, valve 25 in line 26, valve 31 in line 2|, andvalve 28 in line 6, are closed while valve 1 in line 8 is opened, lightproduct from the top of separator 4 then passing over the preconditionedcatalyst in reactor H, the resulting product then being sent toconventional fractionating or condensirg means (not shown) throughopened valve 29 in line 30. Also at this stage, valve i5 is opened andthe conditioning stock passed through line to a reactor ready for theconditioning treatment, a continuous operation bein thus assured.

Because of the heavy nature of the conditioning stock it is readilydecomposed into carbon and other hydrocarbons, and the time required'for accomplishing the conditioning treatment is very short. Forexample, when operating under the conditions described in connectionwith Figure 1, a period of about 2 .5 minutes brings the catalyst to acondition similar to that shown by the catalyst after 5 minutes(Figure 1) where a relatively light gas oil was used as charge. In oneseries of experiments, satisfactory results have been obtained bypassing preheated charge to the separator 4 at a rate of 100 volumes inunit .time, separating it into 80 volumes of overhead and of bottoms,pumping these bottoms at a rate of 20 volumes in unit time through lineit for a time of 2.5 minutes which constitutes the conditioning period,and then passing the overhead from separator 4 to the reactor H at arate of 80 volumes per unit of time for a time of 10 minutes whichconstitutes the conversion or cracking period of the cycle.

If desired, the product withdrawn through line 26 during theconditioning treatment may be recycled in the conditioning operation,for example by introducing this material through line 3| and valve 32.Alternatively, other conditioning materials may be added to the systemthrough line 3| in addition to, or replacing in whole or part materialfrom line l2. Suitable materials for such purposes include non-volatilehydrocarbons such as petroleum pitch, 'coal tar pitch, wax introduced assuch or dissolved in a suitable volatile solvent such as naphtha. Thesematerials may be suitably preheated if desired 'but it should be bornein mind that these are contacted with the catalyst in reactor llimmediately after the. regeneration step under which conditions thecatalyst may be considerably above reaction temperature so that theaddition of conditioning feed at relatively low temperatures may benecessary or desirable to aid in bringing-the catalyst temperature downto the required operating temperature before the conversion or crackingcycle begins. For this reason, in some cases it is necessary to cool theheavy bottoms from separator 4 before using them as a. conditioningmeans.

It is apparent that when using a light charging stock containing littleor no bottoms suitable for conditioning, conditioning materials fromoutside sources must be used. For convenience, stocks suitable for usein the conditioning of catalysts may be termed carbogens.

At the conclusion of the cracking cycle in which the preconditionedcatalyst, prepared as previously described, is employed the regenerationcycle begins. Valve '1 in line 6 is closed as is valve 29 in line 30.Reviviflcation gas enters through valve 33 in line 34 and leaves byvalve 35 in line 36. It is apparent that one complete cycle isdivided'into' three portions (:1) preconditioning (b) cracking and (c)regeneration.

My invention may be further employed in conjunction with the so-calledmoving-bed" type of catalytic cracking operation. In .this type ofoperation, the catalyst is moved through the conversion zone during theconversion period of the cycle, and regenerated in a zone external ofthe conversion zone. Figure 4 illustrates a suitable apparatus and flowprocedure for use in the practice of this embodiment of the invention.Referring to Figure 4, the charge, such as reduced crude or heavy gasoil is introduced by line 4! and pump 42 to furnace 43. The preheatedcharge enters separator 44 by means of line 45. overhead from saidseparator 44 passing to reactor 46 through line 41. The contact materialor catalyst in reactor 46 is constantly moving downward, contactmaterial being added through conveyor 48 and leaving through conveyor49. Converted or cracked hydrocarbons leave reactor 6 through line .50,passing to conventional of vapor therefrom.

Spent catalyst leaving reactor 46 through conveyor 49 is regenerated inany suitable manner, one' suitable form of regenerator beingillustrated. This regenerator 52 contains a plurality of hearths 53, 54,55, 56 and 51, each provided with one or more rakes 58 attached torotatable shaft 59. Spent catalyst falls on the top hearth 53 and isdistributed and agitated by means of the rake or rakes 58 which moveover the surface of said hearth. The catalyst on hearth 53 is graduallymoved down through the regenerator, resting in turn on hearths 54, 55,56 and 51 and is finally discharged into conveyor 46 and moved to thetop of reactor 46 to repeat the cycle.

Means are provided for contacting the catalyst in regenerator 52 withair or dilute air. For example, air or dilute air may pass through ductto to ducts 6|, over the hearths 53, 54 and 55 and out through ducts 52and duct 63. The regenerating fluid may be suitably warmed or cooledbefore entering duct 60 and part or all of the flue gas leaving 63 mayberecycled after eliminating a portion which is replaced by make-up air.

A separate duct 64 is shown supplying hearth 56. Inert material such asoxygen-free flue gas is supplied to duct 64 and may suitably be flue gasfrom duct 63. This inert flue gas is supplied at such a rate that itforms a seal, the inert material forming a partition between hearth 56and hearth 65. While catalyst can fall irom the upper hearth in the lasthearth.

.u onto hearth n and then hearth ll, gaseous products on the hearth "andon hearth II cannot difluse into the space occupied by-hearth ".1 7Gaseous material ,irom hearth 50 may suitably leave by duct 02' openinginto duct 80.

Heavy products from thebottom oi. separator oll where conversion intogasoline is elected in the presence of the catalyst, and the catalyst lsconditioned in accordance with my invention, for use in reactor 95,

' The conversion Products from reactors 00 and 00 are withdrawn throughlines I00 and MI respectively and may be suitably fractionated into tailgas,.'gasoline, recycle stock and tar, in a conventional system ofpartial condensers. or fracmediate vicinity of hearth 01. The sp'rayersor atomizers may suitably form the teeth of the rakes passing overhearth 51. If desired, steam, flue gas, or gaseous hydrocarbons may beemployed to aid in the-vaporization, spraying or atomization oi theheavy material from the'bottom of separator 44. This may be addedthrough line H. The products from hearth 51 may be removed through lineI2- and worked up as desired. By this process the catalyst isconditioned The conditioning treatment may be eilected, wholly orpartly, at other points in the cycle if desired. For example, heavy oilmay be vaporized, atomized or sprayed into conveyor 40 at one or-morepoints or it may be vaporized, sprayed or atomized into the upperportions of reactor 40. As in the embodiment previously described, theheavy oil used in conditioning may be supplemented or replaced bymaterial from sources other than the charge and where the charge iscomparatively light, such outside sources, preferably, are employed.Conditioning oil from said outside sources may enter the cycle throughline I3 and valve II. It will be. noted that the reactor shown in Figure4, differs from that shown in Figure 3 in that, with the former,operations are continuous. While the catalyst in reactor 46 difiers inactivity from top to bottom of said reactor, the integrated activity ofall the material in reactor 46 is always constant regardless of thelength of time the reactor has been on stream.- Accordingly, theprocessed charge leaving reactor 46 by line 50 has constantcharacteristics which are highly advantageous.

A further modified embodiment, also, employinga "moving-bed" type ofcatalytic conversion operation is illustrated in Figure 5. In thisembodiment, a suitable feed stock for the process such as a reducedcrude oil is picked up from source 80 by pump BI and passed throughheater 02 and line 83 into fractionating column 84- where fractionaldistillation of the oil is effected. The non-volatile portion, ii. any,is withdrawn as bottoms through line 85 while the remaining portion isdivided into lightv and heavy fractions which are drawn off throughlines 86 and 81 respectively. The light fraction passing overheadthrough line 86 as a vapor is cooled in exchanger 00; and condensed incondenser 08 and part of the condensate is pumped back from condenser 08by pump 90 to serve as reflux to column 0|. Liquid from condenser 88 ispumped by pump III Through line 92 through a suitable heater 83 and theresultant vapors passed through line 94 to reactor 05. In reactor 95,conversion; to gasoline heated to the reaction temperature required in.reactor 90. The heavieriraction separated in column 04 is withdrawn bypump 00 and passed .through line 81 to heater I0. and thence to heavytionators I02. 1

Hot regenerated catalyst is carried by a conveyor system I03 anddischarged into reactor 99, travelling therethrough from top to bottomand droppin through a star-feeder or solids pump I00 into reactor 05.The catalyst continues downwardly through reactor 95' and dropsthrough'a. I l

, star-feeder or solids pump I015 into regenerator ,I0I wherein theaccumulated impurities are removed by burning with air or other suitableregenerating gas introduced through I08. The hot regenerated catalyst isreturned to reactor 99 through conveyor system I03, and gaseousregeneration products are withdrawn through duct I09.

From the foregoing it will be apparent that the a process thereindescribed. accomplishes the object of my invention of providing aprocess for the-catalytic conversion of hydrocarbons' whereby a morefavorable distribution and enhanced yield of the desired conversionproducts is obtained. It will further be readily apparent to thoseskilled Y in the art that while the invention has been illustrated anddescribed with respect toa preferred operation and examples, and withrefertested, .in vapor form, with an alumina-silica cracking catalystunder reacting conditions adapted to produce the, required extent ofconversion into low-boiling hydrocarbons distilling within the gasolineboiling range, and wherein said. catalyst in the absence of aconditioning treatment exhibits a catalytic activity characterized by aninitial period of gradually increasing yleld'of gasoline per unit oftime up to an optimum value and by the continuous formation of acarbonaceous deposit on the catalyst during said initial period, thesteps, including, separating the hydrocarbon charged into a lightfraction, and a heavy fraction relatively readily heatdecomposable toproduce coke or carbon compared to said light fraction, passing theheavy normally deposited during said initial period, and

then passing the light fraction, in vapor form,

' in contact with said catalyst under reacting conditions adaptedtoproduce the required degree of conversion into low-boiling hydrocarbonsdistilling within the gasoline boiling range.

2. A process of converting high-boiling hydrocarbons to low-boilinghydrocarbons involving contacting said high-boiling hydrocarbons, in thevapor phase. with an alumina-silica cracking catalyst under reactingconditions adapted to' continuously produce a carbonaceous deposit onthe catalyst with consequent relatively short onstream periods and ahigh yield and quality of hydrocarbons distilling within the gasolineboiling range, which comprises preconditionirfg said catalyst prior tothe conversion treatment by passing a relatively readilyheat-decomposable hydrocarbon in contactwith'said catalyst underreacting conditions adapted to decompose it to a mixture of hydrocarbonsand solid carbonaceous material, and in quantity suflicient only todeposit a, coating of carbonaceous hydrocarbon terial on the catalyst inan amount of about 0.5% to 2.0% by weight of the catalyst, and thenpassing vaporized high boiling hydrocarbons relatively stable todecomposition by heat in contact with said preconditioned catalyst underreaction conditions adapted to produce a substantial conversion thereofto low boiling hydrocarbons with in the gasoline boiling range.

3. A process of catalytically cracking high boiling hydrocarbons to lowboiling hydrocarbons within the gasoline boiling range and involving theconcurrent production of a carbonaceous deposit on the catalyst withconsequent relatively short on-stream periods, which comprises forming arelatively small amount of a carbonaceous hydrocarbon deposit on analuminasilica cracking catalyst by passing a relatively readily heatdecomposable hydrocarbon in contact with the catalyst under reactionconditions adapted to decompose the hydrocarbon to volatile hydrocarbonsand carbonaceous material, thereby preconditioning the catalyst andeliminating its tendency to produce excessive coke and fixed gases atthe initial portion of the conversion period, and then passing vaporizedhigh" boiling hydrocarbons relatively stable to decomposition,

by heat in contact with said preconditioned catalyst under reactionconditions adapted to produce a. substantial conversion thereof to lowboiling hydrocarbons within the gasoline boiling range.

4. A process asdefined in claim 3 wherein said readily heat decomposablehydrocarbon com prises a non-volatile fraction of a petroleum crude.

5; In a process of catalytically cracking high boiling hydrocarbons tolow boiling hydrocarbons within the gasoline boiling range, theimprovement which consists in passing a non-volatile readily heatdecomposable fraction of a crude petroleum in contact with analumina-silica cracking catalyst selected from the group consisting ofsynthetic composites of silica-gel and alumina, and activated clays,under reaction conditions adapted to decompose the hydrocarbon tovolatile hydrocarbons and non-vo1atile carbonaceous hydrocarbon materialwith consequent relatively short on-stream periods, therebypreconditioning the catalyst with said non-volatile material andeliminating its tendency to produce excessive coke and fixed gases atthe initial portion or a, subsequent conversion period whereinhydrocarbons are passed over the catalyst to con currently produce lowboiling hydrocarbons within the gasoline boiling range and acarbonaceous deposit on the catalyst.

' ROBERT F. RU'I'HRUFF.

